The present invention relates to radiation image conversion panels and stimulable phosphors, and in particular to radiation image conversion panels and stimulable phosphors exhibiting superior luminance and sharpness.
As an effective means for replacing conventional radiography is known a recording and reproducing method of radiation images using stimulable phosphors described in JP-A No. 55-12148 (hereinafter, the term, JP-A refers to an unexamined and published Japanese Patent Application).
In the method, a radiation image conversion panel (hereinafter, also simply denoted as panel) comprising a stimulable phosphor is employed, and the method comprises the steps of causing the stimulable phosphor of the panel to absorb radiation having passed through an object or having radiated from an object, sequentially exciting the stimulable phosphor with an electromagnetic wave such as visible light or infrared rays (hereinafter referred to as xe2x80x9cstimulating raysxe2x80x9d) to release the radiation energy stored in the phosphor as light emission (stimulated emission), photoelectrically detecting the emitted light to obtain electrical signals, and reproducing the radiation image of the object as a visible image from the electrical signals. The panel having been read out is subjected to image-erasing and prepared for the next photographing cycle. Thus, the radiation image conversion panel can be used repeatedly.
In the radiation image recording and reproducing methods described above, a radiation image is advantageously obtained with a sufficient amount of information by applying radiation to an object at a considerably smaller dose, as compared to conventional radiography employing a combination of a radiographic film and a radiographic intensifying screen. Further, in the conventional radiography, the radiographic film is consumed for every photographing; on the other-hand, in this radiation image converting method, in which the radiation image conversion panel is employed repeatedly, is also advantageous in terms of conservation of resources and economic efficiency.
The radiation image conversion panel (1) employed in the radiation image recording and reproducing method basically comprises a support (3) and provided thereon a phosphor layer (stimulable phosphor layer) (2), provided that, in cases where the phosphor layer is self-supporting, the support is not necessarily required. The stimulable phosphor layer comprises a stimulable phosphor dispersed in a binder. There is also known a stimulable phosphor layer, which is formed by vacuum evaporation or a sintering process, free from a binder, and which comprises an aggregated stimulable phosphor. There is further known a radiation image conversion panel in which a polymeric material is contained in the openings among the aggregated stimulable phosphor. On the surface of the stimulable phosphor layer (i.e., the surface which is not in contact with the support) is conventionally provided a protective layer (4) comprising a polymeric film or an evaporated inorganic membrane to protect the phosphor layer from chemical deterioration and physical shock.
The stimulable phosphor, after being exposed to radiation, produces stimulated emission upon exposure to the stimulating ray. In practical use, phosphors are employed, which exhibit an emission within a wavelength region of 300 to 500 nm stimulated by stimulating light of wavelengths of 400 to 900 nm. Examples of such stimulable phosphors include rare earth activated alkaline earth metal fluorohalide phosphors described in JP-A Nos. 55-12145, 55-160078, 56-74175, 56-116777, 57-23673, 57-23675, 58-206678, 59-27289, 59-27980, 59-56479 and 59-56480; bivalent europium activated alkaline earth metal fluorohalide phosphors described in JP-A Nos. 59-75200, 6-84381, 60-106752, 60-166379, 60-221483, 60-228592, 60-228593, 61-23679, 61-120882, 61-120883, 61-120885, 61-235486 and 61-235487; rare earth element activated oxyhalide phosphors described in JP-A 59-12144; cerium activated trivalent metal oxyhalide phosphors described in JP-A No. 55-69281; bismuth activated alkaline metal halide phosphors described in JP-A No. 60-70484; bivalent europium activated alkaline earth metal halophosphate phosphors described in JP-A Nos. 60-141783 and 60-157100; bivalent europium activated alkaline earth metal haloborate phosphors described in JP-A No. 60-157099; bivalent europium activated alkaline earth metal hydrogenated halide phosphors described in JP-A 60-217354; cerium activated rare earth complex halide phosphors described in JP-A Nos. 61-21173 and 61-21182; cerium activated rare earth halophosphate phosphors described in JP-A No. 61-40390; bivalent europium activated cesium rubidium halide phosphors described in JP-A No. 60-78151; bivalent europium activated cerium halide rubidium phosphors described in JP-A No. 60-78151; bivalent europium activated halogen phosphors described in JP-A No. 60-78153; and tetradecahedral rare earth metal activated alkaline earth metal fluorohalide phosphors which are precipitated from liquid phase, as described in JP-A No. 7-233369.
However, sufficient performance has not been achieved with respect to sharpness and luminance. Specifically in mammography, in order to photograph a mamma comprised of tissues such as a mammary gland, interstitial tissue, fat, blood vessel and skin, which are close in their X-ray absorption coefficient, it is necessary to increase the difference in their X-ray absorption to form a clearer image. To increse the X-ray absorption difference, it is necessary to make X-ray quality more easily absorbable into the organic material to conduct photographing and for that purpose, photographing is conducted using X-rays of a lower tube voltage (i.e., the lower the X-ray tube voltage, the larger difference in X-ray absorption). Conventional chest radiography is generally conducted at a tube voltage of 80 to 140 kV. On the contrary, mammography is conducted using X-rays at a tube voltage of 25 to 32 kV, which are more easily absorbed by the stimulable phosphor. However, emission of the radiation image conversion panel exhibits a characteristic that X-rays of a higher tube voltage result in higher luminance and therefore X-rays of lower tube voltage provide lower luminance. As a result, in mammography of a low tube voltage, X-rays cannot reach the bottom of the plate so that the surface emission mainly plays a role.
Accordingly, it is an object of the present invention to provide a radiation image conversion panel having a stimulable phosphor layer and a stimulable phosphor exhibiting superior luminance and sharpness even in X-ray radiography at a low tube voltage.
The object of the invention can be accomplished by the following constitution:
1. A radiation image conversion panel comprising a support having thereon a stimulable phosphor layer containing a stimulable phosphor and a protective layer, wherein the stimulable phosphor layer exhibits a density of not less than 3.00 g/cm3, the stimulable phosphor layer being provided between the support and the protective layer;
2. The radiation image conversion panel described in 1, wherein the stimulable phosphor layer has a thickness of less than 200 xcexcm;
3. The radiation image conversion panel described in 1, wherein the stimulable phosphor layer exhibits a density of not less than 3.12 g/cm3;
4. The radiation image conversion panel described in 1, wherein the stimulable phosphor is represented by the following formula (1):
(Ba1xe2x88x92x M2x)FX:yEu2+xe2x80x83xe2x80x83formula (1)
wherein M2 is at least an alkaline earth metal selected from the group consisting of Mg, Ca, Sr, Zn and Cd; X is at least a halogen selected from the group consisting of Cl, Br and I; x and y are the number meeting the following requirement:
0xe2x89xa6xxe2x89xa60.6 and 0 less than yxe2x89xa60.2;
5. The radiation image conversion panel described in 4, wherein in formula (1), X is I;
6. The radiation image conversion panel described in 5, wherein the stimulable phosphor is prepared using an aqueous barium iodide solution as a raw material, the aqueous barium iodide solution containing barium iodide of not less than 3 mol/l;
7. The radiation image conversion panel described in 6, wherein the stimulable phosphor exhibits a density of not less than 5.45 g/cm3;
8. The radiation image conversion panel described in 7, wherein the stimulable phosphor exhibits a density of not less than 5.80 g/cm3;
9. The radiation image conversion panel described in 1, wherein the stimulable phosphor layer exhibits a filling factor of not less than 60%;
10. The radiation image conversion panel described in 1, wherein the stimulable phosphor has an average particle size of not more than 5 xcexcm;
11. The radiation image conversion panel described in 1, wherein the stimulable phosphor layer contains a binder, the binder being comprised of a sulfonic acid group containing polyester resin or a sulfonic acid group containing polyurethane resin;
12. A stimulable phosphor exhibiting a density of not less than 5.45 g/cm3;
13. The stimulable phosphor described in 12, wherein the stimulable phosphor exhibits a density of not less than 5.80 g/cm3;
14. The stimulable phosphor described in 12, where the stimulable phosphor is represented by the following formula (1):
(Ba1xe2x88x92x M2x)FX:yEu2+xe2x80x83xe2x80x83formula (1)
wherein M2 is at least an alkaline earth metal selected from the group consisting of Mg, Ca, Sr, Zn and Cd; X is at least a halogen selected from the group consisting of Cl, Br and I; x and y are the number meeting the following requirement:
0xe2x89xa6xxe2x89xa60.6 and 0 less than yxe2x89xa60.2;
15. The stimulable phosphor described in 14, wherein in formula (1), X is I;
16. The stimulable phosphor of claim 15, wherein the stimulable phosphor is prepared using an aqueous barium iodide solution as a raw material, the aqueous barium iodide solution containing barium iodide of not less than 3 mol/l;
17. The stimulable phosphor described in 12, wherein the stimulable phosphor has an average particle size of not more than 5 xcexcm;
18. A radiographic image forming method comprising the step of:
(a) exposing a radiation image conversion panel to radiation through an object,
wherein the radiation image conversion panel comprises a support having thereon a stimulable phosphor layer containing a stimulable phosphor and a protective layer, the stimulable phosphor layer exhibiting a density of not less than 3.00 g/cm3 and the stimulable phosphor layer being provided between the support and the protective layer;
19. The radiographic image forming method described in 18, wherein in step (a), the radiation image conversion panel stores a mammographic image;
20. The radiographic image forming method described in 18, wherein in step (a), the radiation image conversion panel is exposed to a radiation at a tube voltage of not more than 30 kV.
Preferred embodiment of the present invention include:
(1) A radiation image conversion panel comprising a support having thereon a stimulable phosphor layer containing a stimulable phosphor and a protective layer, wherein the stimulable phosphor layer exhibits a density of not less than 3.00 g/cm3;
(2) The radiation image conversion panel described in 1, wherein the stimulable phosphor layer exhibits a density of not less than 3.12 g/cm3;
(3) The radiation image conversion panel described in 1 or 2, wherein the stimulable phosphor is represented by the following formula (1):
(Ba1xe2x88x92x M2x)FX:yEu2+xe2x80x83xe2x80x83formula (1)
wherein M2 is at least an alkaline earth metal selected from the group consisting of Mg, Ca, Sr, Zn and Cd; X is at least a halogen selected from the group consisting of Cl, Br and I; x and y are the number meeting the following requirement:
0xe2x89xa6xxe2x89xa60.6 and 0 less than yxe2x89xa60.2;
(4) The radiation image conversion panel described in 3, wherein in formula (1), X is I;
(5) The radiation image conversion panel described in 4, wherein the stimulable phosphor is prepared using an aqueous barium iodide solution as a raw material, the aqueous barium iodide solution containing barium iodide of not less than 3 mol/l;
(6) The radiation image conversion panel described in 5, wherein the stimulable phosphor exhibits a density of not less than 5.45 g/cm3;
(7) The radiation image conversion panel described in 6, wherein the stimulable phorphor exhibits a density of not less than 5.80 g/cm3;
(8) The radiation image conversion panel described in any of 1 through 7, wherein the stimulable phosphor has an average particle size of not more than 5 xcexcm;
(9) The radiation image conversion panel described in any of 1 through 8, wherein the stimulable phosphor layer contains a binder, the binder being a polyester resin or a polyurethane resin, each of which contains a sulfonic acid group;
(10) A stimulable phosphor exhibiting a density of not less than 5.45 g/cm3;
(11) The stimulable phosphor described in 10, wherein the stimulable phosphor exhibits a density of not less than 5.80 g/cm3 
(12) The stimulable phosphor described in 10 or 11, where the stimulable phosphor is represented by the following formula ( 1):
(Ba1xe2x88x92x M2x)FX:yEu2+xe2x80x83xe2x80x83formula (1)
wherein M2 is at least an alkaline earth metal selected from the group consisting of Mg, Ca, Sr, Zn and Cd; X is at least a halogen selected from the group consisting of Cl, Br and I; x and y are the number meeting the following requirement:
0xe2x89xa6xxe2x89xa60.6 and 0 less than yxe2x89xa60.2;
(13) The stimulable phosphor described in any of 10 through 12, wherein in formula (1), X is I;
(14) The stimulable phosphor described in 13, wherein the stimulable phosphor is prepared using an aqueous barium iodide solution as a raw material, the aqueous barium iodide solution containing barium iodide of not less than 3 mol/l;
(15) The stimulable phosphor described in any of 10 through 14, wherein the stimulable phosphor has an average particle size of not more than 5 xcexcm.